Transom Flex

[Lund86]

Hello<br /><br /> My boat is made for a short shaft motor. It is a 1979 Lund 15 ft Rhino aluminum boat.I recently took off my Evinrude 40 HP 1976 short shaft model and replaced with a 1986 35 hp long shaft merc. I purchased a product from T&R Marine called a transom elevator to raise the engine mount 5 inches.I have everything mounted up and the new bracket is very solid. The question is there is a slight flex to the transom when I put some torgue on the lower part of the motor. Still on land I haven't tried it in the water. Is this slight flex ok or is it something to worry about. I never checked for the flex when I had the 40 on the rig. I never thought to look. I had the 40 on for 3 or 4 summers with narry a problem. Thanks for any input.

 

[Solittle]

Re: Transom Flex

Lund - Best contact Lund for this one. Most manufacturers have "customer service" who try to be helpful. I would be very careful about giving much weight to anything that anyone says to your question. If the flex is, in fact, risky you could be looking at a transom that gives way. That could ruin more than your day IMHO.

 

[FlyBoyMark]

Re: Transom Flex

The motor being long shaft has a greater mechanical lever advantage over the short shaft of five inches plus the addition of the transom jack plate......to put it bluntly you have exceeded the design limits of the torsional strength of the transom...it will break with the setup you have unless you build some braces into it now....in additon the old motor was powerhead rated and worn.....new one is prop rated and more than likely has a higher torq curve.(I believe the Merc your using is a two cylinder looper that used to be power head rated at 40 HP, so its got some kick if its rated at the prop..)

 

[evin300]

Re: Transom Flex

Hey Lund, dont worry too much, as ALL transoms flex (not made of concrete) Instead, keep an eye on the shape of the top of the transom. <br /><br />Sight the width of the transom from port to starboard along the top cap of the transom. Look for the top to start taking a new shape, it will begin to arc aft.<br /><br />This would tell me that the load is to great, and is breaking it down, which would create an arc in the top.<br /><br />Play it safe untill ya feel good about it.

 

[Lund86]

Re: Transom Flex

thanks guys I will take your coments into consideration. One thing the bracket I am using is not a jack plate per se it does not set the motor back. It is a sleve that fits over the transom with a plate on either side of the transom with bolts running through transom, motor bracket and both plates. see picture at. http://www.trmarine.com/cat.html <br />I still have the 40 so either way I will still be "on the water"<br />thanks again

 

[crab bait]

Re: Transom Flex

pretty neet gizmos..

 

[FlyBoyMark]

Re: Transom Flex

Lund..it still does the same thing..increases the fulcrum on the transom.....be very carefull.